Therapeutic applications of miRNAs in myocardial infarction and cardiac regeneration The long-term goal of our study is to understand the cellular and molecular mechanisms that control the proliferation of heart cells (cardiomyocyte). We propose to use microRNAs, a class of small non-coding RNAs, as molecular tools to explore the molecular mechanisms of cardiomyocyte proliferation and cardiac regeneration. We hypothesize that miR-19a/miR-19b are key components of a molecular circuit that controls cardiomyocyte proliferation and cardiac regeneration. The overall goal of this study is to test the therapeutic potential of these miRNAs in repairing damaged hearts. We present two focused yet integrative aims to test our hypothesis: Aim #1. To test the hypothesis that miR-19a/miR-19b plays a key role in cardiac regeneration that can serve as a therapeutic target to repair infarcted hearts. Aim #2. To define the molecular mechanism by which miR-19a/miR-19b repress their targets to protect the damaged hearts. This study will uncover novel components and molecular pathways for the control of cardiomyocyte proliferation and cardiac regeneration.